1. Field of the Invention
The present invention relates to a method of supporting code types, and more particularly, to a method of supporting multiple code types in a wireless mobile communication system.
2. Discussion of the Related Art
In a broadband wireless access system, an Orthogonal Frequency Division Multiple Access (OFDMA) scheme is used to transmit data. When the OFDMA scheme is used, a structure of a frame is defined as follows. First, a downlink frame represents a preamble at the beginning of the frame which can be used for time synchronization between a mobile station (MS) and a base station (BS), and at the same time, for channel equalization in a physical layer. Following the preamble, the frame includes a Downlink Map (DL-MAP) message and an Uplink Map (UL-MAP) message which define location and usage of allocated bursts.
More specifically, the DL-MAP message defines the usage of each burst allocated in the downlink section of the frame. Similarly, the UL-MAP message defines the usage of the burst allocated in the uplink section of the frame. An Information Element (IE), which is included in the DL-MAP, is classified in a downlink traffic section of a user group according to a Downlink Interval Usage Code (DIUC), a Connection Identification (CID), and the location of the burst signal (e.g., sub-channel offset, symbol offset, number of sub-channels and number of symbols).
The use of the IE of the UL-MAP is determined by an Uplink Interval Usage Code (UIUC) per each CID. Moreover, a corresponding location of an uplink traffic section is defined by duration. Here, the usage of each section is determined according to the values of the UIUC used by the UL-MAP. A starting point of each section is offset by an amount of the duration set in the UL-MAP IE from the previous IE starting point.
The MS receives a Downlink Channel Descriptor (DCD) message and an Uplink Channel Descriptor (UCD) message for network entry or to re-enter the network for handover or for other reasons. A cell periodically provides the physical channel characteristics of the downlink and uplink via the DCD/UCD message. Here, the cell can also be used to represent a base station (BS).
The BS configures the Downlink_Burst_Profile based on the received signal qualities of each MS. In other words, the BS uses a Channel Quality Information (CQI) transmitted from each MS and configures the Downlink_Burst_Profile or an Adoptive Modulation and Coding (AMC) according to the channel status of each MS. Alternatively, as a supportive measure, the Downlink_Burst_Profile can be modified or changed by using a Downlink Burst Profile Change (DBPC) request or response, i.e., DBPC-REQIRSP and a ranging request/response (RNG-REQ/RSP) procedures.
FIG. 1 is an example illustrating a threshold value for modifying the burst profile. The MS measures a Signal to Noise Ratio (SINR), for example, C/(N+1), and compares an average value of allowed application scope. The application scope is limited by a threshold level. That is, if the SINR exceeds the allowed application scope, the MS uses a DBPC scheme to request for a new burst profile. Based on whether the MS requests for a more robust profile having stronger interference (e.g., Quadrature Phase Shift Keying) or whether the MS requests for a less robust profile, having less interference (e.g., 64 Quadrature Amplitude Modulation), the BS executes transmission and reception of the message for actual change of the modulation scheme. Here, the term ‘more robust’ means that there is stronger interference, and the term ‘less robust’ means that there is less interference.
According to conventional art, if there is a plurality of code types which can be supported by MS within the scope of services available by the BS, and if downlink/uplink burst profiles are used to support various code types, the intervals (or space) of the SNR corresponding to each AMC increases. Therefore, a modulation scheme that can be provided for one coding type decreases. As a result, the intervals of the threshold values, used for changing the AMC per each coding type, increase, and consequently, there is a problem in properly applying the AMC according to the channel status.